Field emission displays are well known in the art. A field emission display includes an anode plate and a cathode plate that define a thin envelope. Typically, the anode plate and cathode plate are thin enough to necessitate some form of a spacer structure to prevent implosion of the device due to the pressure differential between the internal vacuum and external atmospheric pressure. The spacers are disposed within the active area of the device, which includes the electron emitters and phosphors.
The potential difference between the anode plate and the cathode plate is typically within a range of 300-10,000 volts. To withstand the potential difference between the anode plate and the cathode plate, the spacers typically comprise a dielectric material. Thus, the spacers have dielectric surfaces that are exposed to the evacuated interior of the device.
During the operation of the field emission display, electrons are emitted from the electron emitters, such as Spindt tips or carbon nanotubes, toward the anode plate. These electrons traverse the evacuated region and impinge upon phosphors positioned on the anode plate; however, some of these electrons may strike the dielectric surfaces of the spacers. In this manner, the dielectric surfaces of the spacers become charged. Typically, the dielectric spacers become positively charged because the secondary electron yield of the spacer material is initially greater than one.
Numerous problems arise due to the charging of the dielectric surfaces within a field emission display. For example, control over the trajectory of electrons adjacent to the spacers is lost. Also, the risk of electrical arcing events increases dramatically.
It is known to use electron current from the electron emitters coupled with a fixed resistance connected between the anode plate and an anode voltage source to reduce the voltage at the anode plate and cause the electrons to be attracted by the charged surfaces instead of the anode. The electrons are used to neutralize the charged surfaces. However, the electrons that bounce off of or emit secondarily from the dielectric surface also strike the phosphors, which results in a visible “flash” of light being generated at the viewing screen of the field emission display. Furthermore, the fixed resistance between the anode plate and the anode voltage source necessitates a high current to pull down the anode voltage, which results in large power losses. Conventionally, this discharge is accomplished every frame, resulting in a high current drain and a perceptive “buzz”.
U.S. Pat. No. 6,031,336 disclosed a pull-down circuit integrated on a substrate separate from the substrate containing electron emitters for illuminating the display screen. This patent taught a method of reducing charge accumulation in a field emission display, thereby reducing or eliminating a visible “flash” and reducing the power loss associated with pulling down the anode voltage.
Accordingly, there exists a need for a method for reducing charge accumulation in a field emission display, which reduces or eliminates this visible “flash” and which reduces the power loss associated with repetitively pulling down the anode voltage. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.